Power tools

ABSTRACT

Power tool  1  may include table  5  on which work W is positioned. A portion of a circular blade  3  protrudes above table  5 . Circular blade  3  may be driven by a motor. The motor may be controlled by a control device  90 . Work W is cut by means of an operator sending work W positioned on an upper face of table  5  in the direction of the circular blade  3  while circular blade  3  is being driven by the motor. Power tool  1  may include first radar device  86  and second radar device  87  for monitoring a predetermined area in the vicinity of circular blade  3 . First radar device  86  may detect whether objects other than work are present in the vicinity of a outer edge of circular blade  3 . Second radar device  87  may detect the location of objects moving within the predetermined area in the vicinity of circular blade and detects the speed at which the objects are moving in the direction in which work is sent. Control device  90  may cause an emergency halt of the motor in the case where first radar device  86  detects that an object other than work is present in the vicinity of the outer edge of circular blade  3 . Further, Control device  90  may cause an emergency halt of the motor in the case where an object detected by second radar device  87  has a predetermined positional relationship relative to circular blade  3  and the detected speed exceeds a predetermined value.

CROSS REFERENCE

[0001] This application claims priority to Japanese patent applicationnumber 2002-328837, filed Nov. 12, 2002, and Japanese patent applicationnumber 2003-81399, filed Mar. 24, 2003, each of which are incorporatedherein by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to power tools, e.g., table saws,miter saws and the like. Specifically, techniques are described forpreventing a cutting tool from making contact with objects other thanwork.

[0004] 2. Description of the Related Art

[0005] U.S. unexamined patent application no. 17336/2002 describes apower tool that carries out an emergency stop when a cutting tool hasmade contact with a person (i.e., an object other than work). The knownpower tool includes a contact detection system that detects contactbetween a person and a cutting tool. The contact detection system iselectrically coupled to the cutting tool and monitors an electricalpotential of the cutting tool in order to detect contact between aperson and the cutting tool. If contact between the person and thecutting tool is detected by the contact detection system, power supplyto the motor is stopped, effecting an emergency stop of the cuttingtool.

SUMMARY OF THE INVENTION

[0006] However, in the known power tool, movement of the cutting tool ishalted only after contact between a person and the cutting tool has beendetected, and it is not possible to prevent contact between the personand the moving cutting tool.

[0007] It is, accordingly, one object of the present teachings toprovide improved power tools that can prevent a cutting tool from makingcontact with objects other than work (e.g., persons, etc).

[0008] In one aspect of the present teachings, power tools are taughtthat are capable of detecting abnormal conditions before contact betweenthe cutting tool and objects other than work occurs. Therefore, if theabnormal conditions are detected, the power tools can warn operatorsand/or stop movement of the cutting tool.

[0009] Thus, in one embodiment of the present teachings, power tools mayinclude a cutting tool, such as a circular blade or saw blade, and adrive source, such as an electric motor, for driving the cutting tool.Such power tools may also include a detecting device (e.g., a detectingdevice using radio waves, a detecting device using ultrasonic waves, adetecting device using infrared rays, etc.) and a control device, suchas a microprocessor or processor, in communication with the detectingdevice. For example, the detecting device may detect the location andspeed of objects (e.g., work, etc.) moving within a predetermined areanear the cutting tool. On the basis of the location and speed of theobjects detected by the detecting device the control device maydetermine whether operating conditions are normal or abnormal. Forexample, the control device may determine whether the cutting tool andthe objects detected by the detecting device have a predeterminedpositional relationship (e.g., whether the distance between the cuttingtool and the object is within a predetermined value), and also determinewhether the speed of the objects detected by the detecting devicetowards the cutting tool exceeds a predetermined value. From the resultsof these determinations it may be decided whether operating conditionsare normal or abnormal. For example, when a detected object is moving atnormal speed near the cutting tool and in a direction approaching thecutting tool, it may be determined that this is simply work beingdelivered for cutting at a normal speed and that operating condition isnormal. However, when the detected object is moving at rapid speed nearthe cutting tool and in a direction approaching the cutting tool, it maybe determined that operating conditions is abnormal. Since it can bedetermined whether operating conditions are normal or abnormal beforecontact between the object and the cutting tool occurs, contact betweenthe object and the cutting tool can be prevented under abnormaloperating conditions.

[0010] When operating conditions have been determined to be abnormal, awarning may be given to the power tool operator, and/or the movement ofthe cutting tool may be automatically stopped. For example, the powertools may also include a buzzer that generates a warning sound. Further,the power tool may also include a switch for cutting off power supply tothe motor. As another example, the power tool may also include a brakemechanism that engages and stop the cutting tool, or retractingmechanism that retract the cutting tool from its operating position.Further, the power tool may also include a barrier that is placedbetween the cutting tool and the operator when operating conditions havebeen determined to be abnormal.

[0011] Preferably, the detecting device may include a radar device thattransmits radio waves towards the predetermined area and receives theradio waves reflected therefrom. By using the radio waves, the locationand speed of the object can be detected accurately even if chips areformed during the cutting operation.

[0012] Further, it is preferred that the frequency of the radio wavestransmitted from the radar device is 1 GHz or above, and it is morepreferred that the frequency is in the range of 10˜30 GHz. By usingradio waves of this frequency, directivity can be improved, and it ispossible to monitor only the surroundings of the cutting tool.

[0013] In another embodiment of the present teachings, the power toolsmay further include a table on an upper face of which the work ispositioned. A portion of the cutting tool may protrude above the table,this protruding portion cutting the work. In this case, the area to bemonitored by the radar device may be restricted to above the table. Forexample, it is possible to monitor only an area that rises to apredetermined height above the table and is within a predetermined rangeof distance from side faces of the cutting tool. Further, it ispreferred that the radar device is disposed in positions so as tosandwich the table and face towards a power tool operator. This type ofconfiguration prevents the radar device from obstructing the operationsof the power tool operator.

[0014] In another aspect of the present teachings, power tools mayinclude a cutting tool and a motor for driving the cutting tool. Thepower tool may further include a radar device and a processor incommunication with the radar device. The radar device preferablytransmits radio waves towards a predetermined area in the vicinity of acontacting location where an edge of the cutting tool and work makecontact, and receives radio waves reflected therefrom. The processorpreferably determines from the reflected radio waves received by theradar device whether an object other than work is in the predeterminedarea. For example, using the difference between the waves reflected whenwork is in the predetermined area and the waves reflected when an objectother than work is in the predetermined area, the processor candetermine whether work or an object other than work is in thepredetermined area. When it has been determined that an object otherthan work is in the predetermined area, a warning may be given to thepower tool operator, and/or the movement of the cutting tool may beimmediately stopped. By this means, contact between the cutting tool andan object other than work can be prevented.

[0015] Preferably, the power tools may also include a memory for storingthe reflected radio waves created when the work is disposed within thepredetermined area. The reflected waves can be stored as time seriesdata in the memory. Alternatively, only identification informationextracted from the reflected waves (e.g., peak values of the reflectedwaves, waveform patterns, etc.) may be stored. Further, the processormay determine whether an object other than work is in the predeterminedarea by using the reflected waves received by the radar device and thereflected waves stored in the memory. For example, the processorpreferably determines that an object other than work is in thepredetermined area when the absolute value of the difference between thepeak values of the reflected waves received by the radar device and peakvalues of the reflected waves stored in the memory exceeds apredetermined threshold value. Since the reflected waves created whenthe work is disposed in the predetermined area are already stored, thisconfiguration allows an accurate determination of whether an objectother than work is in the predetermined area.

[0016] Generally, the radio wave reflection coefficient of materialsvaries according to frequency. As a result the radio waves may betransmitted from the radar device as impulses (i.e., including manyfrequency elements), and the processor may perform frequency analysis onthe reflected waveforms to determine whether an object other than workis present within the predetermined area.

[0017] In the alternative, in the case where the work is wood, the radiowave reflection coefficient characteristics of wood can be taken intoaccount and only radio waves within a narrow frequency range can betransmitted (e.g., single frequency radio waves) to allow thedetermination of whether an object other than work is present within thepredetermined area. For example, the frequency of the radio wavestransmitted from the radar device may be established between the rangeof 1˜30 GHz. Radio waves with a frequency of 1˜30 GHz have a lowreflection coefficient for wooden material that has a low moisturecontent, and have a high reflection coefficient for objects with a highmoisture content (e.g., hands, fingers, etc.). Consequently, it ispossible to identify whether the object from which the radio waves arereflected is work or an object other than work (i.e., an object with ahigh moisture content) even though radio waves within a narrow frequencyrange are transmitted. That is, when the peak values of the reflectedwaves received by the radar device exceed a predetermined threshold, itcan be determined that an object other than work is present in thepredetermined area. Further, even in the case where the frequency of theradio waves is within the range of 1˜30 GHz, the frequency may bechanged in accordance with one's aims. For example, it is preferred thata lower radio-wave frequency is chosen for penetrating bulky wood, andthat a higher radio-wave frequency is chosen for improving thedirectivity of the radio waves.

[0018] In another embodiment of the present teachings, the power toolsmay further include a table on an upper face of which the work ispositioned. A portion of the cutting tool may protrude above the table,this protruding portion cutting the work. In this case, it is preferredthat the radar device may be disposed beneath the table and that thetable may have a penetrable window which can allow the radio wavestransmitted from the radar to penetrate therethrough. The penetrablewindow can be manufactured from a material (e.g., resin) through whichradio waves penetrate easily. Locating the radar device beneath thetable prevents the radar device from obstructing the operator.

[0019] In another embodiment of the present teachings, the power toolsmay include a table on an upper face of which work is positioned, and anarm slidably or pivotably attached to the table. A cutting area forcutting the work may be provided on the table. The cutting tool may berotatably attached to the arm. By moving the arm relative to the table,the cutting tool can be moved between an operating position close to thecutting area and a waiting position removed therefrom. In this case, itis preferred that the radar device transmits the radio waves towards thecutting area and receives the radio waves reflected therefrom.

[0020] In another aspect of the present teachings, the radar device mayinclude a radio wave transmitting member and a radio wave receivingmember. Preferably, at least one of the radio wave transmitting memberand the radio wave receiving member may have a plurality of microstripantennas. By using the microstrip antennas, the radio wave transmittingmember or the radio wave receiving member can be miniaturized and cansave space. Further, by using a plurality of microstrip antennas orpatch antennas (i.e., a type of microstrip antenna), the desireddirectivity can be obtained. Further, the radio wave transmitting memberand the radio wave receiving member may have different antennas.Alternatively, the radio wave transmitting member and the radio wavereceiving member may have the same antenna.

[0021] Preferably, the microstrip antenna may include a strip conductor,a ground conductor disposed in a position opposite the strip conductor,and a dielectric layer disposed between the strip conductor and theground conductor. In this case, a groove may be formed in a surface ofthe dielectric layer and that the strip conductor may be disposed withinthe groove. Since the strip conductor does not protrude from the surfaceof the dielectric layer, damage to the strip conductor can be prevented.Further, a groove may be formed in the ground conductor and that thedielectric layer may disposed within the groove formed in the groundconductor. By this means, the dielectric layer does not protrude fromthe ground conductor, and consequently damage to the dielectric layercan be prevented. Preferably, the microstrip antenna may be disposedwithin a surface of a housing of the power tools (e.g., a table, etc.).

[0022] These aspects and features may be utilized singularly or, incombination, in order to make improved power tools, including but notlimited to, table saws, miter saws. In addition, other objects, featuresand advantages of the present teachings will be readily understood afterreading the following detailed description together with theaccompanying drawings and claims. Of course, the additional features andaspects disclosed herein also may be utilized singularly or, incombination with the above-described aspect and features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a partial cross-sectional side view showing a table sawaccording to a first representative embodiment of the present teachings.

[0024]FIG. 2 is a partial cross-sectional plane view of the table sawshown in FIG. 1.

[0025]FIG. 3 schematically shows the positional relationship between acircular blade and a penetrable window.

[0026]FIG. 4 is a block diagram schematically showing a representativecircuit of a first radar device.

[0027]FIG. 5A schematically shows a waveform of an output gate signal ofthe first radar device.

[0028]FIG. 5B schematically shows a waveform of output signal from anoscillation circuit of the first radar device.

[0029]FIG. 5C schematically shows a waveform of a radio wave received bythe first radar device when only wooden work is disposed in a firstpredetermined area.

[0030]FIG. 5D schematically shows a waveform of a radio wave received bythe first radar device when work W and a finger are disposed in thefirst predetermined area.

[0031]FIG. 6 is a block diagram showing a representative circuit of asecond radar device.

[0032]FIG. 7 schematically shows the relationship between frequency andtime of radio waves transmitted from the second radar device.

[0033]FIG. 8 schematically shows an area monitored by the second radardevice.

[0034]FIG. 9 is a block diagram showing a representative circuit of thetable saw of the first embodiment.

[0035]FIG. 10 is a flowchart of a representative process for cutting awork using the table saw.

[0036]FIG. 11 shows the positional relationship between the circularblade and the area monitored by the second radar device divided intozone I, zone II, and zone III.

[0037]FIG. 12A shows a representative example for disposing the secondradar device relative to the table saw of the first representativeembodiment.

[0038]FIG. 12B shows another representative example for disposing thesecond radar device relative to the table saw of the firstrepresentative embodiment.

[0039]FIG. 12C shows another representative example for disposing thesecond radar device relative to the table saw of the firstrepresentative embodiment.

[0040]FIG. 13A shows a representative configuration of a microstripantenna used in a table saw of a second representative embodiment of thepresent teachings.

[0041]FIG. 13B shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0042]FIG. 13C shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0043]FIG. 13D shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0044]FIG. 13E shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0045]FIG. 13F shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0046]FIG. 13G shows another representative configuration of amicrostrip antenna used in the table saw of the second representativeembodiment of the present teachings.

[0047]FIG. 14 schematically shows plane and side views of the table sawof the second representative embodiment.

[0048]FIG. 15 is a cross-sectional view of an antenna member disposedwithin a table of the table saw shown in FIG. 14.

[0049]FIG. 16 schematically shows a representative example of anarrangement of patch antennas disposed within the table.

[0050]FIG. 17 schematically shows another representative example of anarrangement of patch antennas disposed within the table.

DETAILED DESCRIPTION OF THE INVENTION

[0051] First Detailed Representative Embodiment

[0052]FIG. 1 shows a first detailed representative embodiment of thepresent teachings, which is table saw 1 having table 5 on which toposition wooden work W. A portion of circular blade 3 protrudes abovetable 5, and top and sides of this protruding portion are covered byblade guard 7. Blade guard 7 is rotatably attached to table 5 and ispushed open by work W during cutting.

[0053] As shown in FIGS. 1 and 2, a lower portion of circular blade 3may be disposed within blade hood 21 that is attached to table 5 in amanner whereby it can be inclined. Openings 81 and 82 for allowing motorhousing 23 to move up and down are formed in a side face of blade hood21. Motor housing 23 is attached, in a manner whereby up and downmovement is possible, to the side face of blade hood 21 via two guidebars 25 a and 25 b. Motor M is disposed within motor housing 23.Circular blade 3 is attached to a drive shaft of motor M.

[0054] As shown in FIG. 1, splitting blade 9 for preventing the closureof the hole cut in the work W by circular blade 3 may be attached at theposterior of circular blade 3. Splitting blade 9 is fixed to a posteriorend of motor housing 23 by means of bracket 27 fastened by bolts. Thus,as the height to which circular blade 3 is exposed above table 5 changesas motor housing 23 is moved up and down, splitting blade 9 moves up anddown therewith.

[0055] Next, the mechanism for moving motor housing 23 up and down willbe explained. Motor housing 23 may be moved up and down by means ofrotating handle 31 that projects at the anterior of table 5. Shaft 33 ofhandle 31 is the same axis as shaft 37 of inclining dial 35. Bevel gear39 is connected to a tip of shaft 33. Bevel gear 43 engages bevel gear39, bevel gear 43 being connected to a lower end of threaded shaft 41that extends in a longitudinal direction.

[0056] The upper and lower ends of threaded shaft 41 are fixed to bladehood 21, threaded shaft 41 rotating in one spot without moving up ordown. A nut member (not shown) having an inner thread is coupled tothreaded shaft 41, and the nut member is fixed to motor housing 23. As aresult, when handle 31 is rotated, motor housing 23 is moved up or downby means of the thread feed mechanism of threaded shaft 41 and the nutmember. Guide bars 25 a and 25 b function to guide the up-down movementof motor housing 23.

[0057] Next, the mechanism for causing circular blade 3 to incline willbe explained. Blade hood 21 may be inclined by rotating inclining dial35 that has the same axis as handle 31. As shown in FIG. 2, plate 53having arc-shaped gear 51 fixed thereto is attached to an anterior sideof table 5. Arc-shaped slit 55 which follows arc-shaped gear 51 isformed in the plate 53. Shaft 33 of handle 31 passes through slit 55 toan inner side. Pinion gear 57 that engages arc-shaped gear 51 is fixedto shaft 37 of inclining dial 35. As a result, when inclining dial 35 isrotated, pinion gear 57 moves along the arc of arc-shaped gear 51, andblade hood 21 inclines therewith. When blade hood 21 has inclined suchthat circular blade 3 has reached a desired angle, locking lever 83 isoperated to fix blade hood 21.

[0058] As shown in FIG. 1, first radar device 86 and second radar device87 may be disposed at the anterior and posterior respectively ofcircular blade 3. First radar device 86 may monitor a firstpredetermined area that is in the vicinity of a location where an outeredge of circular blade 3 and work W make contact. As shown in FIG. 1,first radar device 86 is disposed to the anterior of circular blade 3below table 5. As shown in FIG. 3, table 5 may have penetrable window 5a, through which radio waves penetrate, near the anterior edge ofcircular blade 3. A plate made from resin may be utilized to formpenetrable window 5 a.

[0059] Second radar device 87 may monitor a second predetermined areathat surrounds the portion of circular blade 3 that protrudes abovetable 5. As shown in FIGS. 1 and 2, second radar device 87 may beattached to the tip of arm 85 attached to the posterior of table 5. Asis clear from the figures, second radar device 87 is disposed above andto the posterior of circular blade 3.

[0060] Next, first radar device 86 and second radar device 87 will beexplained in more detail. First, first radar device 86 will beexplained. FIG. 4 is a block diagram showing a representative circuit ofthe first radar 86. As shown in FIG. 4, first radar device may includeantenna 124 for transmitting and receiving radio waves. Oscillationcircuit 122 for oscillating an electrical signal at a specifiedfrequency and outputting this electrical signal may be connected toantenna 124 (specifically, to a radio wave transmitting member ofantenna 124). Clock circuit 120 may be connected to oscillation circuit122. Clock circuit 120 is a circuit for periodically causing the outputof oscillation circuit 122 to be ON or OFF. Radio waves are transmittedfrom antenna 124 only while clock circuit 120 causes the output ofoscillation circuit 122 to be ON.

[0061] Waveform shaping circuit 132 may be connected to antenna 124(specifically, to a radio wave receiving member of antenna 124) viaamplifying circuit 128 and filter circuit 130. Amplifying circuit 128amplifies the signal of the radio waves received by antenna 124. Filtercircuit 130 filters noise from the signal amplified by amplifyingcircuit 128. Waveform shaping circuit 132 shapes the waveform of thesignal that was output from filter circuit 130, then outputs the shapedsignal to control device 90.

[0062] Preferably, microwaves (i.e., frequency: 3˜30 GHz) may be used inthe radio waves that are output from first radar device 86; in the firstrepresentative embodiment, 10.5 GHz microwaves may be used. The radiowave reflection coefficient of wooden work W and the radio wavereflection coefficient of an object other than work (e.g., a operator'shand or finger, etc.) differ greatly with the radio waves of thisfrequency band, and this difference in radio wave reflectioncoefficients is utilized to enable discrimination between work W andobjects other than work W. Specifically, with radio waves of thisfrequency band, the radio wave reflection coefficient is low with wood,which has a low moisture content, and the radio wave reflectioncoefficient is high with objects having a high moisture content. As aresult, in the first representative embodiment, the strength of the peakvalues of the reflected waves are used to determine whether thereflected waves were reflected from work W or from an object other thanwork which was located above the work W.

[0063] FIGS. 5A˜5D shows radio waves transmitted from first radar device86 together with output waveforms of radio waves received by first radardevice 86. FIG. 5A shows the waveform of an output gate for outputtingthe signal of oscillation circuit 122 to antenna 124. FIG. 5B shows thewaveform of the signal that is actually being output from oscillationcircuit 122 to antenna 124. FIG. 5C shows the output waveform of a radiowave received by first radar device 86 when only wooden work W islocated in the first predetermined area. FIG. 5D shows the outputwaveform of a radio wave received by first radar device 86 when work Wand a finger are located in the first predetermined area.

[0064] As shown in FIG. 5A, the output gate for outputting the signal ofoscillation circuit 122 is ON only for periodic time intervals Tp. As aresult, as shown in FIG. 5B, a signal of 10.5 GHz is output fromoscillation circuit 122 only while the output gate is ON, radio wavesbeing transmitted from the radio wave transmitting member of antenna 124on the basis of this output signal. After the radio waves have beentransmitted from antenna 124, these transmitted radio waves and thereflected radio waves are received by the radio wave receiving member ofantenna 124. In FIGS. 5C and 5D, ‘a’ are waves that were transmittedfrom the radio wave transmitting member and received directly by theradio wave receiving member, ‘b’ and ‘d’ are reflected waves that werereflected from objects in the first predetermined area. As is clear fromthe figures, the reflected waves ‘b’ reflected from work W have a lowpeak voltage, whereas the reflected waves ‘d’ that penetrate work W andare reflected from a finger have a high peak voltage. Consequently, itis possible to determine, on the basis of the peak voltages of thereflected waves received by first radar device 86, whether only work Wor an object other than work W is in the first predetermined area.Furthermore, the distance between first radar device 86 and objectsdetermines the time taken until the reflected waves are observed (i.e.,the period t0˜t1 shown in FIG. 5D). Consequently, the time (t0˜t2) takenfor the reflected waves to be observed by first radar device 86 may bedetermined by the distance between first radar device 86 and the firstpredetermined area. As a result, it is acceptable for the time for firstradar device 86 to observe the reflected waves to be up until t2.

[0065] Next, second radar device 87 will be explained. FIG. 6 is a blockdiagram showing a representative circuit of the second radar 87. Asshown in FIG. 6, second radar device 87 may have antenna 104 fortransmitting and receiving radio waves. Oscillation circuit 102 isconnected to antenna 104 (specifically, to a radio wave transmittingmember of antenna 104), and clock circuit 100 is connected tooscillation circuit 102. Clock circuit 100 periodically transfers thefrequency of the signal that is output from oscillation circuit 102 totwo-phase, and also switches the state of switch 108. As a result, asshown in FIG. 7, the frequency of the signal that is output fromoscillation circuit 102 is periodically (1 period=2×ts) switched from ahigh frequency H to a low frequency L. Further, as the frequency of thesignal that is output from oscillation circuit 102 is switched, circuits(110 a˜114 a and 110 b˜114 b) for processing the signal from a radiowave receiving member of antenna 104 is simultaneously switched.Further, as is clear from FIG. 7, second radar device 87 differs fromfirst radar device 86, in that it continuously transmits radio waves atone of the two frequencies.

[0066] Moreover, diode mixer 106 is connected to antenna 104(specifically, to the radio wave receiving member of antenna 104). Diodemixer 106 is a circuit that mixes the radio waves received by antenna104, that is, the radio waves that are transmitted from the radio wavetransmitting member of antenna 104 and the radio waves that have beenreflected by a reflector, and outputs these mixed waves (i.e., diodemixer 106 is a so-called waveform inspection circuit). The output fromdiode mixer 106 changes on the basis of whether or not a reflector ismoving towards second radar device 87. That is, if the reflector is notmoving, the radio waves reflected by the reflector have the samefrequency as the radio waves transmitted by antenna 104. On the otherhand, due to the Doppler effect, if the reflector is moving, the radiowaves reflected by the reflector have a frequency different from that ofthe radio waves transmitted by antenna 104. As a result, if thereflector is moving, radio waves having two close but differingfrequencies mutually interfere, causing beats to appear in the outputwaveform of diode mixer 106. In second radar device 87 of the firstrepresentative embodiment, the frequency of these beats is used tomeasure the speed of movement of the reflector. Furthermore, the outputfrom diode mixer 106 also differs from the frequency of the radio wavesoutput from antenna 104. In the second radar device 87 of the firstrepresentative embodiment, the phase difference of the beats produced bythe two frequencies of the radio waves created by the reflections fromthe reflector is used to measure the position of the reflector (i.e.,the distance from the second radar device 87).

[0067] Two circuit groups are connected with diode mixer 106 via switch108. That is, the first circuit group may comprise amplifying circuit110 a, filter circuit 112 a and waveform shaping circuit 114 a. Thesecond circuit group may comprise amplifying circuit 110 b, filtercircuit 112 b, and waveform shaping circuit 114 b. The first circuitgroup is connected to diode mixer 106 while antenna 104 is transmittingradio waves at the first frequency, and the second circuit group isconnected to diode mixer 106 while antenna 104 is transmitting radiowaves at the second frequency. The structure and effects of the circuitsis identical with the circuits used in first radar device 86.

[0068] The two waveform shaping circuits 114 a and 114 b are connectedto phase difference measuring circuit 118, whereas only waveform shapingcircuit 114 a is connected to speed measuring circuit 116. Phasedifference measuring circuit 118 is a circuit for measuring the phasedifference of the beats observed when the radio waves of bothfrequencies are transmitted (in other words, measuring the distance ofthe reflector), and speed measuring circuit 116 is a circuit formeasuring the phase difference of the beats observed when the radiowaves of the first frequency is transmitted (in other words, measuringthe speed of the reflector). The output of phase difference measuringcircuit 118 and of speed measuring circuit 116 are both output tocontrol device 90.

[0069] Preferably, radio waves of 1 GHz or above may be used in theradio waves output from second radar device 87; in the firstrepresentative embodiment, 24.2 GHz microwaves may be used. This isbecause it is preferred that second radar device 87 monitors only thesurroundings of circular blade 3. In other words, as shown in FIG. 8,this is because contact with circular blade 3 is unlikely in locationsat a distance greater than a predetermined value (w/2 or greater) fromside faces of circular blade 3. A further reason for using the abovefrequency is that the higher the frequency of radio waves the shorterthe wavelength, which allows the location and speed of the reflector tobe detected accurately. Moreover, the antenna shape and location ofsecond radar device 87 is determined so that the desired directivity(that is, a directivity adequate to observe the second predeterminedarea) can be obtained when radio waves at the above frequencies aretransmitted.

[0070] A representative circuit diagram for controlling table saw 1 willbe explained with reference to FIG. 9. As shown in FIG. 2, controldevice 90, which disposed below table 5 (see FIG. 2), may includemicrocomputer 92 and memory 94 (e.g., EEPROM). Microcomputer 92 maypreferably include a CPU, ROM, RAM and I/O (interface), which arepreferably integrated onto a single integrated circuit chip. The ROM ofmicrocomputer 92 may store programs for automatically stopping thedriving operation of motor M. Memory 94 is connected to microcomputer 92and stores the waveforms observed by first radar device 86 when onlywork W is located in the first predetermined area near the outer edge ofcircular blade 3. The reflected waveforms stored in memory 94 changeeach time the type (e.g., thickness, wood type, etc.) of work W cut bytable saw 1 changes.

[0071] First radar device 86 and second radar device 87 are connected tomicrocomputer 92, and the reflected waveforms output from first radardevice 86, and the speed and location of the reflector output fromsecond radar device 87 are input to the microcomputer 92. Power supplycircuit 98 is connected to motor M via driving circuit 96, and isconnected to microcomputer 92. Power supply circuit 98 is capable ofbeing connected to an external commercial power source, and supplies thepower supplied from this external commercial power source tomicrocomputer 92 and motor M. Further, motor switch 97 for startingmotor M is connected to microcomputer 92.

[0072]FIG. 10 shows a representative method for operating microcomputer92 in order to cut a work using table saw 1. That is, FIG. 10 is aflowchart of the process or program executed by microcomputer 92 duringa cutting operation. In order to cut the work using the table saw 1, theoperator first turns a power switch ON, power supply to themicrocomputer 92 thereby beginning. At this time, motor switch 97 isOFF, consequently circular blade 3 does not begin to rotate.

[0073] When the power switch has been turned ON, as shown in FIG. 10,microcomputer 92 waits until motor switch 97 is turned ON (step S10).The operator first positions the work in the first predetermined area(i.e., the anterior of circular blade 3), then turns the motor switch 97ON. When motor switch 97 has been turned ON (YES in step S10),microcomputer 92 causes first radar device 86 to operate, and receivesthe waveforms of the signals that are output from first radar device 86(step S12). The received waveforms are the reflected waveforms from theradio waves reflected from the work. When the waveforms of the signalsoutput from first radar device 86 have been received, microcomputer 92stores these received waveforms in memory 94 (step S14).

[0074] Further, when motor switch 97 has been turned ON (YES in stepS16), microcomputer 92 outputs a ON signal to driving circuit 96, thisstarting the supply of power to motor M from power circuit 98, andsimultaneously causing the operation of first radar device 86 and secondradar device 87. As a result, circular blade 3 begins to rotate, and themeasured results from first radar device 86 and second radar device 87are periodically output. Microcomputer 92 first reads in the output(i.e., the speed and location of the object moving within the secondpredetermined area) from second radar device 87 (step S18).

[0075] Then, microcomputer 92 determines whether the distance fromsecond radar device 87 to the object, which was read in in step S18, isequal to or greater than a predetermined value 1 (step S20). Thispredetermined value 1 is shorter than the distance from second radardevice 87 to circular blade 3. If the measured distance is below thepredetermined value 1 (NO in step S20), microcomputer 92 quickly stopsmotor M (step S30). Specifically, microcomputer 92 outputs an OFF signalto driving circuit 96, this cutting off the supply of power to motor M.By this means, the rotation of motor M is halted.

[0076] As described above, the driving operation of motor M is haltedwhen the distance measured by second radar device 87 is below thepredetermined value 1 (that is, when an object is between second radardevice 87 and circular blade 3). Motor M is halted in this mannerbecause objects extremely close to second radar device 87 prevent secondradar device 87 from monitoring the surroundings of circular blade 3.

[0077] If the measured distance is equal to or greater than thepredetermined value 1 (YES in step S20), microcomputer 92 determineswhether the distance from second radar device 87 to the object, whichwas read in in step S18, is equal to or less than a predetermined value2 (step S22). This predetermined value 2 is greater than thepredetermined value 1, and is longer than the distance from second radardevice 87 to circular blade 3. If the measured distance exceeds thepredetermined value 2 (NO in step S22), the process proceeds to stepS26. On the other hand, if the measured distance is equal to or belowthe predetermined value 2 (YES in step S22), microcomputer 92 determineswhether the speed of the object read in in step S18 is equal to or lessthan a predetermined speed (step S24). If the speed of the object readin in step S18 is equal to or less than the predetermined speed (YES instep S24), the process proceeds to step S26. If the speed of the objectread in in step S18 exceeds the predetermined speed (NO in step S24),microcomputer 92 quickly stops motor M (step S30).

[0078] Thus, in the case where the object measured by second radardevice 87 is within zone I shown in FIG. 11, (that is, in the case wherethe distance from second radar device 87 is below the predeterminedvalue 1), the driving operation of motor M is halted. In the case wherethe object measured by second radar device 87 is within zone II (thatis, in the case where the distance from second radar device 87 is equalto or above the predetermined value 1 and equal to or less than thepredetermined value 2), motor M is halted only when the speed of theobject exceeds a predetermined speed. Further, in the case where theobject measured by second radar device 87 is within zone III (that is,in the case where the distance from second radar device 87 exceeds thepredetermined value 2), motor M is not halted since the likelihood ofcontact with circular blade 3 is low.

[0079] Microcomputer 92 proceeds to step S26 and takes up the outputwaveforms from first radar device 86. Then, microcomputer 92 determineswhether the absolute value of the difference between the peak values ofthe output waveforms taken up in step S8 (that is, the peak values ofthe reflected waves reflected from the object in the first predeterminedarea) and the peak values of the output waveforms stored in memory 94 instep S2 (that is, the peak values of the reflected waves reflected fromthe work in the first predetermined area) is equal to or below apredetermined value 3 (step S28).

[0080] If the absolute value of the difference between the peak valuesof the two output waveforms is equal to or below the predetermined value3 (YES in step S28), microcomputer 92 determines that an object otherthan work is not present in the first predetermined area, and returns tostep S16. Consequently, if motor switch 97 is in an ON state (YES inStep S16), the process after step S18 is repeated. As a result, therotation of circular blade 3 continues while being monitored by firstradar device 96 and second radar device 87, and the operator can performthe cutting operation by sending the work from the anterior at a safespeed.

[0081] On the other hand, if the absolute value of the differencebetween the peak values of the two output waveforms exceeds thepredetermined value 3 (NO in step S28), microcomputer 92 determines thatan object other than work is present in the first predetermined area,and stops the driving operation of motor M (step S30).

[0082] In summary, in the table saw of the first representativeembodiment, the surroundings of circular blade 3 are monitored by secondradar device 87, and the vicinity of the outer edge of circular blade 3is monitored by first radar device 86, this allowing the possibility ofcontact between circular blade 3 and an object other than work to bedetected before this contact is made, and halting the driving operationof motor M. As a result, it is possible to prevent contact between theobject other than work and the rotating circular blade 3.

[0083] Moreover, only radio waves of a single frequency are transmittedfrom first radar device 86 and second radar device 87. Consequently,antennas 124 and 104 for receiving the reflected waves can be compact,and it is possible to simplify, for example, the amplifying circuit foramplifying the received reflected waves.

[0084] Moreover, in the table saw of the first representativeembodiment, the use of blade guard 7 allows the monitored area nearcircular blade to be restricted, thus limiting the number of radardevices. In other words, by using blade guard 7, all that is monitoredis the movement, in the direction in which work is sent, of objects nearthe circular blade, and only the area near the outer edge of thecircular blade is monitored. As a result, operation becomes safer usingby means of both blade guard 7 and first radar device 86 and secondradar device 87.

[0085] Further, in the first representative embodiment, second radardevice 87 is attached to the tip of the arm attached to table 5.However, second radar device 87 is not restricted to this type ofconfiguration. For example, second radar device 87 may be disposedaccording to the methods shown in FIGS. 12A-12C. In FIG. 12A, arm 85 isattached to the lower portion of the table saw, second radar device 87being attached to the tip of arm 85. Further, FIGS. 12B and 12C showcases where the table saw is fixed to a floor. In FIG. 12B, arm 85 isfixed to a wall to the posterior of the table saw and second radardevice 87 is attached to the tip of arm 85, and in FIG. 12C, arm 85 isfixed to a ceiling and second radar device 87 is attached to the tip ofarm 85.

[0086] Further, in the first representative embodiment, motor Mimmediately halts when the results measured by first radar device 86 andsecond radar device 87 fulfill predetermined conditions. However, aconfiguration is also possible wherein decision criteria are set at twostages; first, the operator is warned when the first stage of thedecision criteria is exceeded, then the driving operation of thecircular blade is halted when the second stage of the decision criteriais exceeded. For example, the region to the anterior of circular blade 3in zone II of FIG. 11 is divided into a further two regions. If it isdetermined that an object is anomalously in the region further fromcircular blade 3, the warning is sounded, and if it is determined thatan object is anomalously in the region closer to circular blade 3, anemergency stop of the motor is performed. With this type ofconfiguration, the operator can be alerted by the warning, thus avoidinginterruptions to the cutting operation.

[0087] Moreover, in the first representative embodiment, singlefrequency radio waves are transmitted from first radar device 86.However, it is also possible that first radar device 86 transmits radiowaves that include all frequencies, such as impulses, and analyzes thefrequencies of the reflected waves to more precisely identify objects inthe first predetermined area.

[0088] Furthermore, in the first representative embodiment, motor Mhalts when it is determined that there is a likelihood of contactoccurring between circular blade 3 and objects other than work. However,it is also possible to provide a retracting mechanism whereby thecircular blade is retracted from above to below the table at times ofemergency, or to provide a brake mechanism that engages and stop thecircular blade at times of emergency.

[0089] Second Detailed Representative Embodiment

[0090] The table saw of the second representative embodiment hassubstantially the same configuration as the table saw of the firstrepresentative embodiment, differing only in using a microstrip antennain place of the antenna 104 of second radar device 87 of the firstrepresentative embodiment. Consequently, in the following descriptiononly the points differing from the first representative embodiment willbe explained.

[0091] First, the configuration of the microstrip antenna will beexplained with reference to FIGS. 13A-13G. As shown in FIG. 13A,microstrip antenna 130 a may comprise strip line 132 a, dielectricsubstrate 134 a, and flat conductor 136 a. Flat conductor 136 a may havean area greater than strip line 132 a. In the case where a body (e.g., atable of a table saw) of a power tool is formed from a conductivematerial (e.g., a metal plate made from aluminum), the body may be usedas the flat conductor 136 a. Flat conductor 136 a is connected to aground. Further, flat conductor 136 a need not necessarily be flat.Dielectric substrate 134 a may be disposed on a surface of flatconductor 136 a. Dielectric substrate 134 a is a plate-shaped dielectricsubstance that utilizes, for example, teflon resin, fiberglass epoxyresin, or the like. In particular, in the case where the frequency ofradio waves to be transmitted and received is 1 GHz or above, teflonresin is preferably utilized. The thickness of the dielectric substrate134 a may be, for example, up to 1 mm. Strip line 132 a may be disposedon a surface 134 s of dielectric substrate 134 a. Strip line 132 a maybe formed from a conductive material, such as, for example, copper foil(thickness up to 35 μm). Strip line 132 a is connected to a feeder line.

[0092] When signals are input to strip line 132 a from an oscillationcircuit, the voltage between strip line 132 a and flat conductor 136 afluctuates. By this means, radio waves are transmitted between stripline 132 a and flat conductor 136 a. The transmitted radio waves aresent to the surface 134 s of dielectric substrate 134 a. Thus,microstrip antenna 130 a may be disposed on the power tool such that theobjects to be measured approach the surface 134 s of dielectricsubstrate 134 a. For example, microstrip antenna 130 a may be disposedon a surface of the power tool opposite the objects to be measured.

[0093] Preferably, the radio waves transmitted from microstrip antenna130 a may be approximately 1 GHz or above. For example, 24.2 GHzmicrowaves may be used. The reason is that having the radio waves at ahigher frequency improves the directivity thereof, allowing the objectsto be measured to be detected with greater accuracy. Furthermore, thefrequency of the radio waves transmitted from microstrip antenna 130 amay be modified so as to be adapted to the properties of the objects tobe measured.

[0094] In the example shown in FIG. 13A, strip line 132 a is copper foiland, due to a surface thereof protruding, may be damaged by abrasion. Inthis case, it is preferred that microstrip antenna 130 a may be disposedwithin a housing of the power tool. Further, the housing may include apenetrable window through which the radio waves transmitted frommicrostrip antenna 130 a penetrate.

[0095] FIGS. 13B˜13G show another example of microstrip antennas. Theexample shown in FIG. 13B utilizes strip conductor 132 b in place ofstrip line 132 a in FIG. 13A. Strip conductor 132 b may be formed from aconductive material (e.g., a metal plate made from aluminum). The use ofstrip conductor 132 b increases the strength thereof against abrasion orimpact. In this case, it is preferred that microstrip antenna 130 b maybe disposed on the surface of the power tool. Furthermore, microstripantenna 130 b may have a certain degree of thickness (e.g., up to 1 mm).As a result, it is possible to form a groove in dielectric substrate 134b and to dispose strip conductor 132 b within this groove. When stripconductor 132 b is in a disposed state within the groove, it ispreferred that a surface of strip conductor 132 b extends along the sameplane as a surface of dielectric substrate 134 b.

[0096] In the example shown in FIG. 13C, dielectric substrate 134 c doesnot have a thickness sufficient to provide a groove therein.Consequently, the portions of dielectric substrate 134 c not havingstrip conductor 132 c disposed thereon may have a filling material 138 cdisposed thereon. Filling material 138 c allows a surface of stripconductor 132 c and a surface of Filling material 138 c to extend alongone plane. Filling material 138 c may be preferably an insulatingmaterial, and a material with little dielectric loss. Filling material138 c may be formed from, for example, resin, cement, or the like.

[0097] Further, in cases where it is not desirable to provide a widthlike that of dielectric substrate 134 b in the example shown in FIG.13B, or a width like that of filling member 138 c in the example shownin FIG. 13C, configurations like those shown in FIGS. 13D and 13E arealso possible. That is, in the example shown in FIG. 13D, a groove maybe formed in flat conductor 136 d, and dielectric substrate 134 d andstrip conductor 132 d may be disposed within the groove. By this means,the area of a surface of dielectric substrate 134 d can be reduced.Similarly, in the example shown in FIG. 13E, flat conductor 136 e mayhave a groove, dielectric substrate 134 e and strip conductor 132 e maybe disposed within the groove, and remaining portions may be filled withfilling material 138 e.

[0098] Moreover, the configurations shown in FIGS. 13F and 13G are alsopossible. In the examples shown in FIGS. 13F and 13G, side walls of flatconductors 136 f and 136 g are inclined faces 137 f and 137 g. In thiscase, the radio waves that are transmitted are easily delivered at theside with inclined faces 137 f and 137 g, and a desirableelectromagnetic field (i.e., detecting area) can be formed.

[0099] The microstrip antennas configured as described above may bedisposed in a table surface of the table saw. FIG. 14 shows an exampleof an arrangement wherein a microstrip antenna is disposed in a surfaceof table 144. Located in the surface of table 144 shown in FIG. 14 are:a transmitting and receiving device 152 for transmitting and receivingradio waves; and a plurality of microstrip antennas or patch antennas154 a˜154 d (hereafter referred to simply as patch antennas).Transmitting and receiving device 152 fulfils the functions of thecircuits 100, 102, 106, 108, 110 a, 110 b, 112 a, 112 b, 114 a, 114 b,116, and 118 shown in FIG. 6. Transmitting and receiving device 152 maybe disposed to the posterior (i.e., the direction opposite the operatorside) of circular blade 142. Patch antennas 154 a˜154 d are a type ofmicrostrip antenna and fulfill the functions of antenna 104 shown inFIG. 6. Two each of the patch antennas 154 a˜154 d may be disposed onleft and right sides of circular blade 142, being separated from oneanother in an anterior-posterior direction.

[0100]FIG. 15 is a cross-sectional view of patch antenna 154 a. As shownin FIG. 15, patch antenna 154 a comprises strip or patch 156 (hereafterreferred to simply as patch), dielectric substrate 158, and table 144.That is, patch 156 corresponds to the strip conductor of FIGS. 13A-13G,dielectric substrate 158 corresponds to the dielectric substrate ofFIGS. 13A-13G, and table 144 corresponds to the flat conductor of FIGS.13A-13G.

[0101] A groove is formed in table 144, and dielectric substrate 158 isdisposed within this groove. Further, a groove is formed in dielectricsubstrate 158, and patch 156 is disposed within this groove. As is clearfrom FIG. 15, surfaces of table 144, dielectric substrate 158, and patch156 all extend along one plane. As a result, patch 156 or dielectricsubstrate 158 do not form an obstruction when the work is slid acrossthe table 144. Moreover, by being disposed within table 144, patchantenna 154 a does not obstruct a design where mechanisms are disposedbeneath table 144 (e.g., a inclining mechanism for inclining circularblade 142, etc.). Further, remaining patch antennas 154 b, 154 c, and154 d may have the same configuration as patch antenna 154 a describedabove.

[0102] As shown in FIG. 14, transmitting and receiving device 152 andpatch antennas 154 a˜154 d are connected with a feeder line L. Feederline L may include two phase shifters 156 a. That is, one of phaseshifters 156 a is disposed between patch antenna 154 a and patch antenna154 c, and other phase shifter 156 a is disposed between patch antenna154 b and patch antenna 154 d. By this means, as shown in the figure onthe right in FIG. 14, the transmitting and receiving direction of theradio waves of patch antennas 154 a˜154 d is altered towards theoperator. As a result, radar device 150 can monitor objects to bemeasured that move in the area surrounding circular blade 142 protrudingabove table 144 (particularly the area towards the operator).Furthermore, the dimensions, number, location, etc. of patch antennas154 a˜154 d may be adapted to correspond to the characteristics of theobjects to be measured.

[0103] As is clear from the above description, using the microstripantenna allows the antenna to be miniaturized, and allows the antenna tobe disposed in the surface of the power tool. By this means, a greaterdegree of design freedom can be obtained concerning the location of theantenna.

[0104] The second representative embodiment described above can beembodied with a variety of transformations or improvements thereto. Forexample, in the example shown in FIG. 16, transmitting device 170 isdisposed to the posterior of circular blade 142 and receiving device 176is disposed to the anterior of circular blade 142. Transmitting device170 may include transmitting machine 174 and patch antennas 172 a and172 b, these being connected via a feeder line L. Further, receivingdevice 176 may include receiving machine 180 and patch antennas 178 aand 178 b, these being connected via a feeder line L. This type ofconfiguration allows the detection of objects to be measured betweentransmitting device 170 and receiving device 176 (that is, in thevicinity of circular blade 142).

[0105] Further, as shown in FIG. 17, it is also possible to locatetransmitting and receiving device 184 to the posterior of circular blade142, and to locate patch antennas 186 a˜186 c, and 188 a˜188 c to theleft and right sides respectively of circular blade 142. In other words,the location, number, etc. of the patch antennas can be varied.Moreover, in the second representative embodiment, the microstripantenna is used in the antenna of a radar device(corresponding to secondradar device 87 of the first representative embodiment) that detects theobjects to be measured by means of Doppler radar. However, themicrostrip antenna may be used in a different type of radar (forexample, first radar device 86 in the first representative embodiment).

[0106] Although the first and the second representative embodiment havebeen described in terms of a table saw, the present teachings cannaturally be applied to other power tools, such as a miter saw, aslide-type table saw, a slide-type circular saw, etc.

[0107] Further, a detecting device which performs radio wave sensing bymeans of a microstrip antenna have been described in detail above.However, this type of detecting device can also be applied to the powertools described below.

[0108] The detecting device described above can also be applied to ademolition hammer. During operation, the vibration of a demolitionhammer causes the vibration of not only the tool, but also of theoperator's body. In particular, if the vibration is great, the head ofthe operator is also caused to vibrate. On the other hand, the forcewith which the hammer strikes the work can be reduced, therebydecreasing the vibration transmitted to the operator; however, in thiscase, operating efficiency falls as the force with which the hammerstrikes the work is reduced. To deal with this problem, the vibration,etc. being transmitted to the operator's head can be detected by meansof the detecting device, and a structure can be formed for canceling thevibration. Specifically, the demolition hammer may include acounter-balance and a canceling mechanism for canceling the vibrationtransmitted to the operator via the counter-balance. The demolitionhammer may further include the detecting device which, by means oftransmitting radio waves towards the operator, detects the movement ofthe operator relative to the hammer. Doppler radar, for example, can beused as the radio wave sensing method. Further, an antenna (e.g., amicrostrip antenna) of the detecting device can be disposed in alocation from where the radio waves can be transmitted towards theoperator. For example, the antenna may be disposed within an upper faceof a housing. The demolition hammer may further include a control devicethat can control the canceling mechanism in response to the vibration ofthe operator's head, the vibration having been detected by the detectingdevice. Moreover, a pick up may be disposed separately within thehousing, measured values from this pick up and the detected values fromthe detecting device being compared, and the counter-balance beingadjusted appropriately.

[0109] The detecting device described above can be applied to a jig saw.The jig saw cuts wood by pressing the wood against an inner face of ashoe and moving the jig saw while the wood is in this state. The cuttingload varies according to the moisture content and thickness of the wood.Accordingly, the moisture content and thickness of the wood can bedetected by means of the detecting device and the detected values usedas feedback for the rotation speed of a motor, thereby improving cuttingoperation. Specifically, a microstrip antenna may be disposed within theinner face (preferably, in a cutting direction viewed from saw blade) ofthe shoe. The method of radio wave sensing may be, for example, a pulsemethod whereby radio waves are transmitted in pulses, and the reflectedwaves therefrom are received. A control device may determine themoisture content or the thickness of the work on the basis of peakvalues of the reflected waves received by the microstrip antenna. Thecontrol device then controls the rotation speed of the motor inaccordance with this moisture content and thickness. Furthermore, themoisture content and thickness may be displayed to the operator by meansof an indicator or the like. Further, in the case where the saw blade ison the point of cutting the support for the work, or foreign materialssuch as nails etc. are discovered, a warning may be given and the motorhalted.

[0110] The detecting device described above can be utilized forpreventing the theft of power tools (e.g., a compressor). That is, amicrostrip antenna can be disposed within an upper face of a housing ofthe compressor. Doppler radar, for example, can be used as the method ofradio wave sensing. Power for the microstrip antenna can be suppliedfrom a battery that can be removably attached to the compressor. If aperson approaches the compressor, or tries to move the compressor, thisis detected by the microstrip antenna, an alarm is sounded, and thecompressor is disabled. By this means, the theft of the compressor canbe prevented. On the other hand, the owner of the compressor carries atransmitter. When the compressor receives radio waves transmitted fromthis transmitter, the alarm is not sounded, and the compressor is notdisabled.

[0111] Finally, although the preferred representative embodiment hasbeen described in detail, the present embodiment is for illustrativepurpose only and not restrictive. It is to be understood that variouschanges and modifications may be made without departing from the spiritor scope of the appended claims. In addition, the additional featuresand aspects disclosed herein also may be utilized singularly or incombination with the above aspects and features.

1. A power tool, comprising: a cutting tool; a motor for driving thecutting tool; means for detecting the location of objects moving withina predetermined area in the vicinity of the cutting tool and fordetecting the speed of approach of the objects towards the cutting tool;and a processor in communication with the detecting means, wherein theprocessor determines whether the object detected by the detecting meanshas a predetermined positional relationship relative to the cutting tooland determines whether the detected speed exceeds a predetermined value.2. A power tool as in claim 1, further comprising a table, wherein aportion of the cutting tool protrudes above the table, wherein thecutting tool cuts the work positioned on an upper face of the table. 3.A power tool as in claim 1, wherein the processor stops the motor whenthe processor determines that the object detected by the detecting meanshas the predetermined positional relationship relative to the cuttingtool and that the detected speed exceeds the predetermined value.
 4. Apower tool as in claim 1, wherein the detecting means comprises a radarfor transmitting radio waves towards the predetermined area and forreceiving waves reflected therefrom.
 5. A power tool as in claim 4,wherein the radar is disposed in a position such that the cutting toolis sandwiched therebetween, and such that the radar faces the operator.6. A power tool as in claim 4, wherein the frequency of the radio wavestransmitted from the radar is 1 GHz or above.
 7. A power tool as inclaim 6, wherein the frequency of the radio waves transmitted from theradar is within the range of 10˜30 GHz.
 8. A power tool as in claim 4,wherein the radar comprises a radio wave transmitting member and a radiowave receiving member, at least one of the radio wave transmittingmember and the radio wave receiving member including one or a pluralityof microstrip antennas.
 9. A power tool as in claim 8, wherein themicrostrip antennas comprises: a strip conductor; a ground conductordisposed in a position facing the strip conductor; and a dielectriclayer disposed between the strip conductor and the ground conductor. 10.A power tool as in claim 9, wherein the dielectric layer has a groove,and the strip conductor is disposed within the groove of the dielectriclayer.
 11. A power tool as in claim 10, wherein the ground conductor hasa groove, and the dielectric layer is disposed within the groove of theground conductor.
 12. A power tool as in claim 11, further comprising atable, wherein a portion of the cutting tool protrudes above the table,wherein the cutting tool cuts the work positioned on an upper face ofthe table, wherein the microstrip antenna is disposed within a surfaceof the table.
 13. A power tool, comprising: a cutting tool; a motor fordriving the cutting tool; a radar for transmitting radio waves towards apredetermined area in the vicinity of a contacting location, this beinga location wherein a blade edge of the cutting tool and work makecontact, and for receiving radio waves reflected therefrom; and aprocessor in communication with the radar, wherein the processordetermines based upon the reflected waves received by the radar whetheran object other than work is in the predetermined area.
 14. A power toolas in claim 13, wherein the processor stops the motor when the processordetermines that an object other than work is in the predetermined area.15. A power tool as in claim 14, further comprising a memory, whereinthe memory stores the reflected radio waves created when the work islocated within the predetermined area, wherein the processor determineswhether an object other than work is in the predetermined area by usingthe reflected waves received by the radar and the reflected radio wavesstored in the memory.
 16. A power tool as in claim 15, wherein theprocessor determines the presence of an object other than work in thepredetermined area when the absolute value of the difference between thepeak values of voltages of the reflected waves received by the radar andpeak values of voltages of the reflected radio waves stored in thememory exceeds a predetermined threshold value.
 17. A power tool as inclaim 16, wherein the work is wooden material and wherein the frequencyof the radio waves transmitted from the radar is within the range of1˜30 GHz.
 18. A power tool as in claim 17, further comprising a table,wherein a portion of the cutting tool protrudes above the table, whereinthe cutting tool cuts the work positioned on an upper face of the table.19. A power tool as in claim 18, wherein the radar is disposed beneaththe table, wherein the table comprises a penetrable window, thepenetrable window allowing the radio waves transmitted from the radar topenetrate therethrough.